The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
Referring to FIG. 1 of French Patent No. 1 152 078, a turboprop engine with an unducted fan comprises a turboprop engine 1 and an annular nacelle 3, disposed coaxially with respect to the turboprop, around a longitudinal axis 5 of the turboprop engine.
The turboprop engine 1 comprises, from the upstream (on the left on FIG. 1) towards the downstream (on the right on FIG. 1) in the flow direction of the air, a compressor, a combustion chamber, a turbine with two counter-rotating rotors (these elements, housed in the nacelle 3, are not visible on this figure) and a nozzle 7 for ejecting the air flow crossing the turboprop engine. These upstream and downstream rotors each drive in rotation around the longitudinal axis 5 an upstream 9a and downstream 9b assembly of fan blades 9 located downstream of the turboprop engine 1.
The nozzle 7 for ejecting the air flow is called rotary, in that it is movable in rotation around the longitudinal axis 5 of the turboprop engine 1, with respect to a gas ejecting cone 10 substantially concentric with the nozzle 7. To this end, and as is visible more particularly on FIG. 2 schematically illustrating the nozzle 7 in longitudinal section, the upstream section 11 of the nozzle 7 is connected to a set of flanges 12, 13 respectively secured to the downstream rotor of the turboprop engine turbine (not represented) and rotary cowls assembled around fan blades 9b (visible on FIG. 1).
As represented on FIG. 2, the nozzle 7, has a substantially triangular longitudinal section. The nozzle 7 comprises an inner wall 15 and an outer wall 17, each typically produced in Inconel.
The inner 15 and outer 17 walls are connected to each other thanks to a circular welding 19 extending over the entire circumference of the nozzle and defining an annular junction area 21 between the inner and outer walls downstream of the nozzle.
According to another type of nozzle, such as that illustrated on FIG. 3 representing a non-rotary nozzle for ejecting the primary air flow of a by-pass turbojet engine, the junction area between the inner 15 and outer 17 walls of the nozzle 7 comprises an annular wedge 23 disposed at the downstream section of the nozzle, between said inner and outer walls. The annular wedge 23 is sandwiched between the inner and outer walls. The annular wedge 23 is brazed on the inner wall 15 and assembled by riveting on the outer wall 17.
The purpose of the rotary and non-rotary nozzles allows the ejection of the hot air flow emanating from the turboprop engine.
However, whatever the type of nozzle retained, these nozzles generally have an annular junction area at the downstream section thereof. The hot air flow flowing along the inner wall of the nozzle diffuses heat between the inner and outer walls of the nozzle, thus leading to limiting the cooling capacities of the engine.
U.S. Pat. No. 2,599,879 provides an annular junction area between the inner and outer walls of the nozzle, constituted by an annular partition having openings through which ducts pass in which cold air circulates.
The advantage of this solution is to refresh the engine. However, the setting up of these ducts is particularly complex and considerably increases the mass of the nozzle.